In June 1959, Swiss Patent no. 338146 disclosed a slip coupling in which a wheel, represented in FIG. 1, comprises rigid arms 1 whose ends 2 form a circle whose diameter is equal to the diameter of a spindle to be inserted at the center of the wheel. These rigid arms 1 are themselves provided with radial extensions serving as inwardly directed elastic arms 3. Once the wheel is mounted on the spindle, the elastic arms 3 produce a frictional engagement between the wheel and the spindle.
In February 2006, that is to say almost half a century later, it was proposed to use an opening having a slightly different shape. Thus, European Patent Application no. EP 1 826 634 made publically available the micromechanical part represented in FIG. 2. This micromechanical part comprises an alternating arrangement of stiffening/positioning areas 4 and elastically deformable areas consisting of tongues 5 whose ends 6 penetrate into the opening while extending beyond the theoretical contour of the spindle, thereby providing a clamping function when the spindle is driven into place. The objective was to allow a driving-fit assembly on a spindle or a stud without the risk of fracture.
The openings having the shapes described in the aforementioned patent documents would appear quite capable of reducing the risk of fracture, but they are unsatisfactory, particularly because they do not make it possible to obtain simultaneously a low assembly (driving) force and a high clamping force (the latter being manifested by a high transmission torque before the part starts to slip on the spindle).